DC power system for marine vessels

ABSTRACT

An embodiment of the invention is a power system for a marine vessel including a plurality of power sources. A propulsion power distribution unit is coupled to the plurality of primary power sources. A plurality of propulsion devices are coupled to the propulsion power distribution unit. A weaponry power distribution unit is coupled to the propulsion power distribution unit. A plurality of directed energy weapons are coupled to the weaponry power distribution unit.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. provisional patentapplication serial No. 60/411,660 filed Sep. 18, 2002, the entirecontents of which are incorporated herein by reference.

BACKGROUND

[0002] The invention relates to DC power systems and is related to U.S.patent application Ser. No. 09/870,897, the entire contents of which areincorporated herein by reference, U.S. patent application Ser. No.10/186,768, the entire contents of which are incorporated herein byreference, U.S. patent application Ser. No. 10/231,330, the entirecontents of which are incorporated herein by reference and U.S.provisional patent application serial No. 60/385,685, the entirecontents of which are incorporated herein by reference.

[0003] The electric service on marine vessels typically comprises two ormore diesel powered generators paralleled together on a common ACelectric bus. While there is a great body of experience withconventional power plants in marine service, maintaining stability of anAC system is quite complex; all generators must remain in phase. ACgenerator stability issues include hunting, maximum power—pullout angle,effects of faults, out-of-phase transfers, and load transients. For besteffect, generating sources must be independent; AC generators insynchronization are not independent. Also, reactive AC, or theout-of-phase portion of the AC wave, does no useful work. Inherent toconventional marine power plants is the pervasiveness of reactive powerthat can reduce resulting voltage, heat equipment and wires, and wasteenergy.

SUMMARY OF THE INVENTION

[0004] An embodiment of the invention is a power system for a marinevessel including a plurality of power sources. A propulsion powerdistribution unit is coupled to the plurality of primary power sources.A plurality of propulsion devices are coupled to the propulsion powerdistribution unit. A weaponry power distribution unit is coupled to thepropulsion power distribution unit. A plurality of directed energyweapons are coupled to the weaponry power distribution unit.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005]FIGS. 1A and 1B depict a power system in one embodiment of theinvention.

DETAILED DESCRIPTION

[0006]FIGS. 1A and 1B depict a power system in an embodiment of theinvention. The power system provides high availability (24×7×forever);computer grade electricity to land based mission critical business andindustrial processes. The system may be adapted for use on naval vesselsto provide an electric infrastructure that greatly improves overallperformance, reliability, and survivability.

[0007] The power system uses a redundant array of independent devices(“RAID”) architecture, to integrate multiple, independent, on-site powergenerators of any type (e.g., fuel cells, gas reciprocating engines, gasturbines, etc.), rotary power conditioners (motor generators), andflywheels by means of a water cooled DC link to create an ultrareliable, computer grade power system. The power system technologyincludes rectifier topology, failsafe controls, a DC disconnect capableof interrupting 6 k amps without arcing, and a unique over voltageprotection device. The power system has no single point of failure andis extremely fault tolerant. The science of probabilistic riskassessment (“PRA”) determines the number of redundant components in aspecific installation. The design balances redundancy against theinherent problem of complexity to arrive at an optimal and simple systemdesign.

[0008] Referring to FIG. 1A, primary power sources 20 generate AC powerthat feeds a propulsion power distribution unit. Primary power sources20 may be any known power source such as fuel cells, gas reciprocatingengines, gas turbines, etc. The propulsion power distribution unitincludes two DC rails 22 and 24 coupled by rungs 26A, 26B and 26C. Eachrung 26 is fed power by each of the primary power sources 20 throughAC-DC converters 28. The power system takes the AC output of eachprimary power source 20 into separate, independent rectifiers andchanges the power to DC that supplies the dual rail, DC propulsion powerdistribution unit. Voltage on the DC link system is tightly controlled(e.g., to 550 volts). Each rung 26 is coupled to a propulsion motor 30which imparts motion to the vessel. Within each rung 26, disconnects 32straddle feeds in and out of the rung 26. This allows components or evenan entire rung 26 to be isolated for service, upgrade, etc.

[0009] Using a DC propulsion power distribution unit eliminates theissues of paralleling AC outputs from multiple generating sources, takesaway the possibility of single points of failure, and eliminatesinter-dependencies among generation sources, negating the potential forcascade failures. Reverse power flow may be blocked by diodes; lowvoltage or phasing on one generating source cannot affect others. The DCpropulsion power distribution unit allows independent control of realpower from each source thereby eliminating reactive power issues at thegenerator.

[0010] The DC propulsion power distribution unit provides DC power to aweaponry power distribution unit. The weaponry power distribution unitincludes two DC rails 42 and 44 coupled by rungs 46A, 46B and 46C. Eachrung 46 is fed power by one of rungs 26A-26C through DC-DC converters48. Each rung 46 is coupled to directed energy weaponry 50. Within eachrung 46, disconnects 52 straddle feeds in and out of the rung 46. Thisallows components or even an entire rung 46 to be isolated for service,upgrade, etc. An energy storage device 54, such as a superconductingmagnetic energy storage device, is coupled to each rung 46.

[0011] The DC propulsion power distribution unit is also connected to anauxiliary power distribution unit shown in FIG. 1B. The auxiliary powerdistribution unit includes two DC rails 62 and 64 coupled by rungs66A-66G. Rung 26B is coupled to rung 66B through DC-DC converter 68A.Rung 26A is coupled to rung 66D through DC-DC converter 68B. Rung 26C iscoupled to rung 66F through DC-DC converter 68C. Each rung 66 alsoreceives power from multiple auxiliary power sources 70 which generateAC power and are coupled to one or more rungs 66 though AC-DC converters72. Auxiliary power sources 70 may be any known power source (e.g., fuelcells, gas reciprocating engines, gas turbines, etc.). AC loads 74 maybe connected to each rung through DC-AC converters 76 (e.g.,motor-generators). DC-AC converter 76 output may be 480 VAC with thevoltage tolerance parameters that IEEE Standard 446-1987 specifies forcomputer equipment. The DC-AC converter 76 clears faults and handlesinrush current demands from the loads. The DC-AC converters 76 alsosupplies reactive power close to the load allowing the prime generatingsources to operate at a high power factor. Solid state variable speeddrives may be used to convert the 550 VDC to 480 VAC for poweringchillers, fans, and pumps.

[0012] DC loads 78 may be connected to each rung through DC-DCconverters 80. DC-DC converter 80 may be employed to buck the DC linkvoltage to 48 VDC at the point of use for telecom loads.

[0013] Within each rung 66, disconnects 82 straddle feeds in and out ofthe rung 66. This allows components or even an entire rung 66 to beisolated for service, upgrade, etc. Ancillary power sources 84 (e.g.,flywheels, batteries) are coupled to one or more rungs 66 to stabilizesystem voltage and mitigate the effects of faults, generating sourcefailures, and load transients.

[0014] Each load, whether DC or AC, is isolated from other systemoutputs by AC-DC converter or DC-DC converter. Therefore, an electricalevent on one circuit cannot propagate to any other circuit.

[0015] While at sea in non-combat conditions, in addition to poweringthe main propulsion motors 30 via the 20 kVDC propulsion powerdistribution unit, the primary power sources 20 supply power to the 600VDC auxiliary power distribution unit and the weapon power distributionunit. During battle conditions the auxiliary power sources 70 would bebrought on line so that all of the power from the primary power sourceswould be available to the main propulsion motors 30 and directed energyweaponry 50.

[0016] The energy storage device 54 supplies high intensity power burststo the directed energy weapons 50, which could be high-energy microwaveor laser based weapons. Energy storage device 54 may be charged usingregenerative braking techniques. While in port, the primary powersources 20 are shut down and an appropriate number of auxiliary powersources 70 supply power requirements. The number of primary powersources 20 and auxiliary power sources 70 depends upon the redundancyneeded to achieve the desired level of availability.

[0017] The power system of FIGS. 1A and 1B allow compact power sourcessuch as rotary engines to be used for the auxiliary power sources 70.The auxiliary power sources 70 as well as the primary power sources 20may be disbursed strategically throughout the ship. This enhancessurvivability; power would be available to both parts even if the shipwere to be cut completely in two. In an emergency, the system can beconfigured so that the main propulsion motors 30 are powered from theauxiliary power distribution unit, albeit at a reduced power rating. Byusing the DC systems described herein, ship designers realizesignificant space and weight savings in a vessel's electricinfrastructure while effecting a substantial improvement in reliability,availability, and survivability.

[0018] The power system does not subscribe to an “N+2” or similarsimplistic redundancy criteria. The power system is designed to meetspecific availability and reliability requirements, and to eliminatesingle points of failure. Redundant units are added as required based onthe PRA evaluation. Units that fail more frequently (e.g., enginegenerators) will require a larger degree of redundancy than morereliable components (e.g., motor generators). Simplistic “N+1” or “2N”redundancy criteria typically spend far too much on some redundantsystems while simultaneously providing too little redundancy for others.The result is a needlessly complex system that costs more, is difficultto operate and maintain, and as a result is more likely to fail. Inembodiments of the power system, redundancy is balanced against theinherent problem of complexity to arrive at a system design that meetssystem requirements at a minimum cost. The quantitative approach to thisarea results in the user being able to make informed decisions aboutredundancy, spare parts inventory, operating tactics, serviceagreements, and staffing levels.

[0019] The propulsion power distribution units may be implemented usinga superconducting DC bus operating at ±10 kV and up to 10 kA. This busis suitable for conveying power from multiple remote sources to theship's drive systems and to the various directed energy weapons 50 andenergy storage device 54. The bus design includes cooling and thermalmanagement systems. Emphasis may be placed on making the bus small,rugged, and requiring extremely little or no maintenance throughout itsoperating lifetime.

[0020] Rectifiers and inverters employed in AC-DC converters, DC-ACconverters and DC-DC converters in the power system may use SCRtechnology because of the technology's proven field reliability andextraordinary ruggedness. The power system may use water cooling tominimize module size and weight. Cryogenic cooling (typically withliquid nitrogen, to 77 degrees Kelvin) offers several potentialadvantages for DD(X) applications. First, cryogenic cooling reducesresistive losses in copper components by a factor of six, resulting inimproved efficiency at the high drive power levels, and/or substantiallyreduced footprint by virtue of greatly reduced electrical interconnectsize.

[0021] Second, cryocooling offers the potential of allowing the SCRs tohandle extremely large momentary overloads, as the maximum junctiontemperature limits will remain unchanged at approximately 400 Kelvin.When cooled at or near room temperature, junction temperature riseduring an electrical fault or pulsed power operation (for firingdirected energy weapons 50) is limited to at most 100 Kelvin. Withcryogenic cooling, the maximum junction temperature rise will exceed 300Kelvin. The SCR's ability to safely conduct such large overloads willallow the rectifiers to electronically control faults, continue tooperate with some devices damaged or destroyed, while the good heattransfer characteristics of boiling liquid nitrogen permits a rapidrecovery to normal operating temperatures.

[0022] Third, cryocooling substantially reduces the difficulty ofconnecting hot power sources to a superconducting bus andsuperconducting motors. Cryocooled rectifiers and motor drives operatebetween the room temperature equipment and the superconductingmaterials. Their large cold mass and relatively small conductorcross-sections (enabled by the 6× reduction in copper resistivity)greatly simplify the design of the transition to superconductingtemperatures, and reduce consumption of precious liquid helium.

[0023] Disconnects 32, 52 and/or 82 may be implemented usingcryogenically cooled arcless DC switches and circuit breakers. The powersystem may include DC switches rated at 6 kA and capable of interruptingfull rated current with no arc. This technology may be extended tocryogenic rectifiers and superconducting DC bus. Existing switches havea size of 32″×24″×18″, approximately {fraction (1/10)} the volume ofconventional switches utilizing arc chutes. Cryogenic cooling couldfurther reduce the size (although mechanical forces developed by largefault currents may limit the amount of reduction possible) and willcertainly extend the maximum permissible fault current that the devicecan safely interrupt.

[0024] While preferred embodiments have been shown and described,various modifications and substitutions may be made thereto withoutdeparting from the spirit and scope of the invention. Accordingly, it isto be understood that the present invention has been described by way ofillustration and not limitation.

What is claimed:
 1. A power system for a marine vessel, the power systemcomprising: a plurality of primary power sources; a propulsion powerdistribution unit coupled to said plurality of primary power sources, aplurality of propulsion devices coupled to said propulsion powerdistribution unit, said propulsion devices imparting motion to saidvessel; a weaponry power distribution unit coupled to said propulsionpower distribution unit; a plurality of directed energy weapons coupledto said weaponry power distribution unit.
 2. The power system of claim 1wherein: said propulsion power distribution unit is a DC powerdistribution unit and includes two rails connected by a plurality ofpropulsion rungs.
 3. The power system of claim 2 wherein: each of saidprimary power sources is coupled to one of said plurality of propulsionrungs.
 4. The power system of claim 2 wherein: each of said primarypower sources is coupled to each of said plurality of propulsion rungsthrough an AC-DC converter.
 5. The power system of claim 2 wherein: eachof said plurality of propulsion rungs is coupled to a respectivepropulsion device.
 6. The power system of claim 2 wherein: said weaponrypower distribution unit is a DC power distribution unit including tworails connected by a plurality of weaponry rungs.
 7. The power system ofclaim 6 wherein: each of said propulsion rungs is coupled to one of saidplurality of weaponry rungs.
 8. The power system of claim 7 wherein:each of said propulsion rungs is coupled to one of said plurality ofweaponry rungs through a DC-DC converter.
 9. The power system of claim 6wherein: each of said plurality of weaponry rungs is coupled to arespective directed energy weapon.
 10. The power system of claim 2further comprising: an auxiliary power distribution unit coupled to saidpropulsion power distribution unit.
 11. The power system of claim 10wherein: said auxiliary power distribution unit is a DC powerdistribution unit including two rails connected by a plurality ofauxiliary rungs.
 12. The power system of claim 11 wherein: each of saidpropulsion rungs is coupled to one of said plurality of auxiliary rungs.13. The power system of claim 12 wherein: each of said propulsion rungsis coupled to one of said plurality of auxiliary rungs through a DC-DCconverter.
 14. The power system of claim 11 wherein: each of saidplurality of auxiliary rungs is coupled to a respective auxiliary load.15. The power system of claim 11 further comprising: an ancillary powersource coupled to at least one of said auxiliary rungs.
 16. The powersystem of claim 15 wherein: said ancillary power source is a flywheel.